It will be the most Catholic Congress ever that hears from Pope Francis — and, as of this month, the first with as many Republican as Democratic members of the church.

Two decades ago, the year before Speaker John A. Boehner initially became part of the GOP leadership and started working to arrange a papal visit, 27 percent of lawmakers were Roman Catholic but only a third of them were Republicans like him. One generation and a pair of papacies later, the Ohioan’s vision is about to become a reality in a Capitol with very different faith demographics.

While the nation and its federal legislators have become more religiously diverse overall, the congressional Catholic population has grown steadily: 31 percent of today’s lawmakers say they belong to the church, but only 22 percent of their constituents do. And the expansion of the papal flock on the Hill has been disproportionately on the Republican side of the aisle. That was underscored by the most recent special election, which sent Darin LaHood to the House as the newest congressman from downstate Illinois. He becomes the 83rd Roman Catholic in the GOP ranks — matching exactly the number of Democrats in the 114th Congress who recognize the pope as their spiritual leader.

Such parity between the parties has looked inevitable for decades, says Michael Sean Winters, a senior journalist at the National Catholic Reporter and the author of “ Left at the Altar: How Democrats Lost the Catholics and How Catholics Can Save the Democrats.”

“When the Democrats became obsessed with identity politics, a large group of white working-class people felt abandoned and started checking out the other team,” he says. “The election of so many more Republican Catholics in recent years is one result.”

A symbolic reflection of the new equality will appear on TV screens worldwide on Sept. 24, when Francis transforms the House chamber’s rostrum into a papal pulpit for the first time. Sitting behind him will be a Catholic titular president of the Senate, Democratic Vice President Joseph R. Biden Jr.; alongside Boehner, who is continuing his religion’s modern dominance of the speakership. (Six of the 11 people elected to preside over the House since World War II have been Catholic; a seventh, Republican Newt Gingrich, held the post as a Baptist but has since converted.)

Arrayed before the pontiff at the joint meeting of Congress will be a legislative elite with a decided Catholic tilt, only in part because the GOP runs both chambers. No matter how emphatically the Vatican and the American leadership describe the historic visit as disconnected from the domestic political agenda, the pool camera cutaway shots of the audience will subliminally pose a powerful rhetorical question: Which party is being run by “better” Catholics, the Republicans under the command of conservatives focused on promoting personal liberty and the sanctity of life, or Democrats under the control of progressives committed to environmental stewardship and combating income inequality?

In the four corners of the leadership, only the Senate Republican team is without a prominent Catholic face. In the House GOP high command, Boehner is joined by Majority Whip Steve Scalise of Louisiana and his chief deputy, Patrick T. McHenry of North Carolina, as well as GOP Conference Secretary Virginia Foxx, also from North Carolina.

Among the Democrats, House Minority Leader Nancy Pelosi is joined at the top table by Caucus Chairman Xavier Becerra, also of California, and his deputy, Joseph Crowley of New York, Steering and Policy Co-Chairwoman Rosa DeLauro of Connecticut, and campaign organization boss Ben Ray Luján of New Mexico. Minority Whip Richard J. Durbin of Illinois and Caucus Secretary Patty Murray of Washington are the Catholics in the eight-person Senate Democratic leadership.

Beyond them, eight of the 41 congressional committees are chaired by a GOP member of the church, while 11 Democratic Catholics serve as ranking committee members.

Protestants initially dominated American public life and their denominations continue to collectively hold a majority of congressional seats even as their claim on the U.S. population has shrunk to just under half. Episcopalians, for example, held 2 of every 5 seats when the First Congress convened in 1789 and still claim 7 percent of the congressional membership despite dwindling to 2 percent of all American adults. The other religion that’s similarly over-represented on the Hill is Judaism; Jews are also 2 percent of the U.S population but hold 5 percent of the seats in the 114th .

(The biggest under-representation? Twenty percent of Americans say they are religiously unaffiliated, but only 2 percent of lawmakers — just 10 of them — say likewise.)

Catholicism became the plurality religion of Congress more than half a century ago, after a wave of politically ambitious members of families recently emigrated from Europe rose all the way through the ranks of the Democratic machines in the Northeast and many big cities of the Midwest.

The culture of American Catholics, like that of Episcopalians and Jews, “has put a high value on education, and better-educated people tend to end up on career paths that end up in public service,” Winters says.

The two churches closest to the Capitol are both Catholic parishes started in the middle of the 19th century: St. Peter’s is a block east of the Cannon Building on the House side, and St. Joseph’s just across from the Hart Building parking lot on the Senate side.

But the faith is curiously under-represented on the roster of 106 congressional chaplains. The only Catholic who’s ministered to the Senate served in 1833. Just two Catholic priests have held the post in the House: The incumbent since 2011, the Rev. Patrick J. Conroy, a Jesuit like the pope, and his predecessor, the Rev. Daniel P. Coughlin, chosen in 2000 after a bitter and monthslong partisan feud in which the Democrats accused the GOP leadership of anti-Catholic bias.

Of all the fights between the parties these days, that allegation has become so manifestly without merit that it’s no longer part of the polarizing agenda.